Chapter 3 The Molecules of Cells

Transcription

1 Chapter 3 The Molecules of Cells PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE TAYLOR SIMON DICKEY HOGAN Lecture by Edward J. Zalisko

2 Introduction Most of the world s population cannot digest milkbased foods. These people are lactose intolerant, because they lack the enzyme lactase. This illustrates the importance of biological molecules, such as lactase, in the daily functions of living organisms.

3 Figure Chapter 3: Big Ideas Introduction to Organic Compounds Carbohydrates Lipids Proteins Nucleic Acids

4 INTRODUCTION TO ORGANIC COMPOUNDS

5 3.1 Life s molecular diversity is based on the properties of carbon Almost all the molecules a cell makes are composed of carbon bonded to other carbons and atoms of other elements. Carbon-based molecules are called organic compounds.

6 3.1 Life s molecular diversity is based on the properties of carbon By sharing electrons, carbon can bond to four other atoms and branch in up to four directions. Methane (CH 4 ) is one of the simplest organic compounds. Four covalent bonds link four hydrogen atoms to the carbon atom. Each of the four lines in the formula for methane represents a pair of shared electrons.

7 Figure 3.1a H H H C H The four single bonds of carbon point to the corners of a tetrahedron.

8 3.1 Life s molecular diversity is based on the properties of carbon Methane and other compounds composed of only carbon and hydrogen are called hydrocarbons. Carbon, with attached hydrogens, can form chains of various lengths.

9 3.1 Life s molecular diversity is based on the properties of carbon A carbon skeleton is a chain of carbon atoms that can differ in length and be straight, branched, or arranged in rings.

10 3.1 Life s molecular diversity is based on the properties of carbon Compounds with the same formula but different structural arrangements are called isomers.

11 Animation: L-Dopa

12 Animation: Carbon Skeletons

13 Animation: Isomers

14 Figure 3.1b-0 Ethane Length: Carbon skeletons vary in length. Double bond Propane 1-Butene 2-Butene Double bonds: Carbon skeletons may have double bonds, which can vary in location. Butane Branching: Carbon skeletons may be unbranched or branched. Isobutane Cyclohexane Benzene Rings: Carbon skeletons may be arranged in rings. (In the abbreviated ring structures, each corner represents a carbon and its attached hydrogens.)

15 Figure 3.1b-1 Ethane Propane Length: Carbon skeletons vary in length.

16 Figure 3.1b-2 Butane Isobutane Branching: Carbon skeletons may be unbranched or branched.

17 Figure 3.1b-3 Double bond 1-Butene 2-Butene Double bonds: Carbon skeletons may have double bonds, which can vary in location.

18 Figure 3.1b-4 Cyclohexane Benzene Rings: Carbon skeletons may be arranged in rings. (In the abbreviated ring structures, each corner represents a carbon and its attached hydrogens.)

19 3.2 A few chemical groups are key to the functioning of biological molecules The unique properties of an organic compound depend on the size and shape of its carbon skeleton and the groups of atoms that are attached to that skeleton. The sex hormones testosterone and estradiol (a type of estrogen) differ only in the groups of atoms highlighted in Figure 3.2.

20 Figure Testosterone Estradiol

21 Figure Testosterone Estradiol

22 Figure 3.2-2

23 Figure 3.2-3

24 3.2 A few chemical groups are key to the functioning of biological molecules Table 3.2 illustrates six chemical groups important in the chemistry of life. The first five groups are called functional groups; they affect a molecule s function in a characteristic way. These five groups are polar, so compounds containing them are typically hydrophilic (waterloving) and soluble in water.

25 3.2 A few chemical groups are key to the functioning of biological molecules A sixth group, a methyl group, consists of a carbon bonded to three hydrogen atoms, is nonpolar and not reactive, but still affects molecular shape and thus function.

26 Table 3.2-0

27 Table 3.2-1

28 Table 3.2-2

29 3.2 A few chemical groups are key to the functioning of biological molecules The functional groups are hydroxyl group a hydrogen bonded to an oxygen, carbonyl group a carbon linked by a double bond to an oxygen atom, carboxyl group a carbon double-bonded to both an oxygen and a hydroxyl group, amino group a nitrogen bonded to two hydrogen atoms and the carbon skeleton, and phosphate group a phosphorus atom bonded to four oxygen atoms.

30 3.3 Cells make large molecules from a limited set of small molecules There are four classes of molecules important to organisms: 1. carbohydrates, 2. lipids, 3. proteins, and 4. nucleic acids.

31 3.3 Cells make large molecules from a limited set of small molecules The four classes of biological molecules contain very large molecules. They are often called macromolecules because of their large size. They are also called polymers because they are made from identical or similar building blocks strung together. The building blocks of polymers are called monomers.

32 3.3 Cells make large molecules from a limited set of small molecules Monomers are linked together to form polymers through dehydration reactions, which remove water. Polymers are broken apart by hydrolysis, the addition of water. These reactions are mediated by enzymes, specialized macromolecules that speed up chemical reactions in cells.

33 Animation: Polymers

34 3.3 Cells make large molecules from a limited set of small molecules A cell makes a large number of polymers from a small group of monomers. For example, proteins are made from only 20 different amino acids and DNA is built from just four kinds of monomers called nucleotides. The monomers used to make polymers are essentially universal.

35 Figure Short polymer Dehydration reaction forms a new bond Unlinked monomer H 2 O Hydrolysis breaks a bond H 2 O Longer polymer

36 Figure Short polymer Unlinked monomer

37 Figure Short polymer Unlinked monomer Dehydration reaction forms a new bond H 2 O Longer polymer

38 Figure

39 Figure Hydrolysis breaks a bond H 2 O

40 CARBOHYDRATES

41 3.4 Monosaccharides are the simplest carbohydrates Carbohydrates range from small sugar molecules (monomers) to large polysaccharides. Sugar monomers are monosaccharides, such as those found in fructose, glucose, and honey.

42 Figure 3.4a

43 3.4 Monosaccharides are the simplest carbohydrates Monosaccharides can be hooked together by dehydration reactions to form more complex sugars and polysaccharides.

44 3.4 Monosaccharides are the simplest carbohydrates The carbon skeletons of monosaccharides vary in length. Glucose and fructose are six carbons long. Others have three to seven carbon atoms. Monosaccharides are the main fuels for cellular work and used as raw materials to manufacture other organic molecules.

45 Figure 3.4b Glucose Fructose

46 3.4 Monosaccharides are the simplest carbohydrates Many monosaccharides form rings. The ring diagram may be abbreviated by not showing the carbon atoms at the corners of the ring and drawn with different thicknesses for the bonds, to indicate that the ring is a relatively flat structure with attached atoms extending above and below it.

47 Figure 3.4c Structural formula Abbreviated structure Simplified structure

48 3.5 Two monosaccharides are linked to form a disaccharide Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction. The disaccharide sucrose is formed by combining a glucose monomer and a fructose monomer. The disaccharide maltose is formed from two glucose monomers.

49 Animation: Disaccharides

50 Figure Glucose Glucose

51 Figure Glucose Glucose H 2 O Maltose

52 3.6 CONNECTION: What is high-fructose corn syrup, and is it to blame for obesity? Most sodas and fruit drinks contain high-fructose corn syrup (HFCS). Fructose is sweeter than glucose. To make HFCS, glucose atoms are rearranged to make the glucose isomer fructose.

53 3.6 CONNECTION: What is high-fructose corn syrup, and is it to blame for obesity? High-fructose corn syrup (HFCS) is used to sweeten many beverages, consists of about 55% fructose and 45% glucose, and is a mixture with about the same proportions as in sucrose. Most scientific studies have not shown health consequences associated with replacing sucrose with HFCS.

54 3.6 CONNECTION: What is high-fructose corn syrup, and is it to blame for obesity? Although HFCS consumption has declined somewhat in recent years, obesity rates continue to rise, with almost 36% of U.S. adults now considered obese. Good health is promoted by a diverse diet of proteins, fats, vitamins, minerals, complex carbohydrates, and exercise.

55 Figure 3.6

56 3.7 Polysaccharides are long chains of sugar units Polysaccharides are macromolecules, polymers composed of thousands of monosaccharides. Polysaccharides may function as storage molecules or structural compounds.

57 3.7 Polysaccharides are long chains of sugar units Starch is a polysaccharide, composed of glucose monomers, and used by plants for energy storage. Glycogen is a polysaccharide, composed of glucose monomers, and used by animals for energy storage.

58 3.7 Polysaccharides are long chains of sugar units Cellulose is a polymer of glucose and forms plant cell walls. Chitin is a polysaccharide, used by insects and crustaceans to build an exoskeleton, and found in the cell walls of fungi.

59 Figure Starch granules in a potato tuber cell Starch Glycogen granules in muscle tissue Glucose monomer Glycogen Cellulose microfibrils in a plant cell wall Cellulose molecules Cellulose Hydrogen bonds

60 Figure Starch granules in a potato tuber cell Starch Glucose monomer

61 Figure Glycogen granules in muscle tissue Glycogen

62 Figure Cellulose microfibrils in a plant cell wall Cellulose molecules Cellulose Hydrogen bonds

63 Figure 3.7-4

64 3.7 Polysaccharides are long chains of sugar units Polysaccharides are usually hydrophilic (waterloving). Bath towels, for example, are often made of cotton, which is mostly cellulose, and therefore water absorbent.

65 Animation: Polysaccharides

66 LIPIDS

67 3.8 Fats are lipids that are mostly energystorage molecules Lipids are water insoluble (hydrophobic, or water-fearing) compounds, are important in long-term energy storage, contain twice as much energy as a polysaccharide, and consist mainly of carbon and hydrogen atoms linked by nonpolar covalent bonds.

68 3.8 Fats are lipids that are mostly energystorage molecules Lipids differ from carbohydrates, proteins, and nucleic acids in that they are not huge molecules and not built from monomers. Lipids vary a great deal in structure and function.

69 3.8 Fats are lipids that are mostly energystorage molecules We will consider three types of lipids: 1. fats, 2. phospholipids, and 3. steroids. A fat is a large lipid made from two kinds of smaller molecules: glycerol and fatty acids.

70 3.8 Fats are lipids that are mostly energystorage molecules A fatty acid can link to glycerol by a dehydration reaction. A fat contains one glycerol linked to three fatty acids. Fats are often called triglycerides because of their structure.

71 Animation: Fats

72 Figure 3.8a Glycerol H 2 O Fatty acid

73 Figure 3.8b

74 Figure 3.8c-0 Saturated fats Unsaturated fats

75 Figure 3.8c-1 Saturated fats

76 Figure 3.8c-2 Unsaturated fats

77 3.8 Fats are lipids that are mostly energystorage molecules Some fatty acids contain one or more double bonds, forming unsaturated fatty acids. These have one fewer hydrogen atom on each carbon of the double bond. These double bonds cause kinks or bends in the carbon chain, preventing them from packing together tightly and solidifying at room temperature. Fats with the maximum number of hydrogens are called saturated fatty acids.

78 3.8 Fats are lipids that are mostly energystorage molecules Unsaturated fats are referred to as oils. Most animal fats are saturated fats. Hydrogenated vegetable oils are unsaturated fats that have been converted to saturated fats by adding hydrogen. This hydrogenation creates trans fats, which are associated with health risks.

79 3.9 SCIENTIFIC THINKING: Scientific studies document the health risks of trans fats In the 1890s, the process of adding hydrogen atoms to unsaturated oils was developed to reduce spoilage of oils, help oils withstand repeated heating for frying, and reduce consumption of animal fats, thought to be less healthy than partially hydrogenated vegetable oils. By the 1990s, partially hydrogenated oils were common in cookies, crackers, snacks, baked goods, and fried foods.

80 3.9 SCIENTIFIC THINKING: Scientific studies document the health risks of trans fats Recent research has shown that trans fats pose an even greater health risk than saturated fats. One study estimated that eliminating trans fats from the food supply could prevent up to one in five heart attacks! In 2006, the U.S. Food and Drug Administration required the listing of trans fat on food labels. Many cities and states have passed laws to eliminate trans fats in unlabeled foods served in restaurants and schools. An increasing number of countries have banned trans fats.

81 3.9 SCIENTIFIC THINKING: Scientific studies document the health risks of trans fats Experimental studies have tested the health risks of consuming trans fats. In experimental controlled feeding trials, the diets of participants contained different proportions of saturated, unsaturated, and partially hydrogenated fats. For ethical and practical reasons, controlled feeding trials are usually fairly short in duration, involve only limited dietary changes, generally use healthy individuals, and measure intermediary risk factors, such as changes in cholesterol levels, rather than actual disease outcomes.

82 3.9 SCIENTIFIC THINKING: Scientific studies document the health risks of trans fats Observational scientific studies on dietary health effects can extend over a longer time period, use a more representative population, and measure disease outcomes and risk factors.

83 3.9 SCIENTIFIC THINKING: Scientific studies document the health risks of trans fats The Nurses Health Study began in 1976 with more than 120,000 female nurses and is an example of an observational study on dietary health.

84 3.9 SCIENTIFIC THINKING: Scientific studies document the health risks of trans fats The results indicate that for each 5% increase in saturated fat, there was a 17% increase in the risk of heart disease and for each 2% increase in trans fat, there is a 93% increase in risk. Trans fats are indeed a greater health risk than saturated fats.

85 Table 3.9-0

86 Table 3.9-1

87 Table 3.9-2

88 3.10 Phospholipids and steroids are important lipids with a variety of functions Phospholipids are the major component of all cell membranes. Phospholipids are structurally similar to fats. Fats contain three fatty acids attached to glycerol. Phospholipids contain two fatty acids attached to glycerol.

89 Figure 3.10 Phosphate group Glycerol Hydrophilic heads Water Hydrophobic tails Symbol for phospholipid Water

90 Figure 3.10a Phosphate group Glycerol Hydrophilic heads Hydrophobic tails

91 3.10 Phospholipids and steroids are important lipids with a variety of functions Phospholipids cluster into a bilayer of phospholipids. The hydrophilic heads are in contact with the water of the environment and the internal part of the cell. The hydrophobic tails cluster together in the center of the bilayer.

92 Figure 3.10b Hydrophilic heads Water Hydrophobic tails Symbol for phospholipid Water

93 3.10 Phospholipids and steroids are important lipids with a variety of functions Steroids are lipids in which the carbon skeleton contains four fused rings. Cholesterol is a common component in animal cell membranes and a starting material for making steroids, including sex hormones.

94 Figure 3.10c

95 3.11 CONNECTION: Anabolic steroids pose health risks Anabolic steroids are synthetic variants of the male hormone testosterone that are abused by some athletes with serious consequences, including violent mood swings, depression, liver damage, cancer, high cholesterol, and high blood pressure.

96 PROTEINS

97 3.12 Proteins have a wide range of functions and structures Proteins are involved in nearly every dynamic function in your body and very diverse, with tens of thousands of different proteins, each with a specific structure and function, in the human body. Proteins are composed of differing arrangements of a common set of just 20 amino acid monomers.

98 3.12 Proteins have a wide range of functions and structures Probably the most important role for proteins is as enzymes, proteins that serve as catalysts and regulate virtually all chemical reactions within cells.

99 3.12 Proteins have a wide range of functions and structures Other types of proteins include transport proteins embedded in cell membranes, which move sugar molecules and other nutrients into your cells, defensive proteins, such as antibodies of the immune system, signal proteins such as many hormones and other chemical messengers that help coordinate body activities,

100 3.12 Proteins have a wide range of functions and structures Other types of proteins include (continued) receptor proteins, built into cell membranes, which receive and transmit signals into your cells, contractile proteins found within muscle cells, structural proteins such as collagen, which form the long, strong fibers of connective tissues, and storage proteins, which serve as a source of amino acids for developing embryos in eggs and seeds.

101 3.12 Proteins have a wide range of functions and structures The functions of different types of proteins depend on their individual shapes. A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds. The amino acid sequence causes the polypeptide to assume a particular shape.

102 Figure 3.12a Groove

103 Figure 3.12b Groove

104 Figure 3.12c

105 3.12 Proteins have a wide range of functions and structures If a protein s shape is altered, it can no longer function. In the process of denaturation, a protein unravels, loses its specific shape, and loses its function. Proteins can be denatured by changes in salt concentration, changes in ph, or high heat.

106 3.13 Proteins are made from amino acids linked by peptide bonds Amino acids all have an amino group and a carboxyl group (which makes it an acid). Also bonded to the central carbon is a hydrogen atom and a chemical group symbolized by R, which determines the specific properties of each of the 20 amino acids used to make proteins.

107 Figure 3.13a Amino group Carboxyl group

108 3.13 Proteins are made from amino acids linked by peptide bonds Amino acids are classified as either hydrophobic or hydrophilic.

109 Figure 3.13b Hydrophobic Hydrophilic Leucine (Leu) Serine (Ser) Aspartic acid (Asp)

110 3.13 Proteins are made from amino acids linked by peptide bonds Amino acid monomers are linked together in a dehydration reaction, joining the carboxyl group of one amino acid to the amino group of the next amino acid, and creating a peptide bond. Additional amino acids can be added by the same process to create a chain of amino acids called a polypeptide.

111 Figure 3.13c-1 Carboxyl group Amino group Amino acid Amino acid

112 Figure 3.13c-2 Carboxyl group Amino group Dehydration reaction Peptide bond Amino acid Amino acid H 2 O Dipeptide

113 3.14 VISUALIZING THE CONCEPT: A protein s functional shape results from four levels of structure A protein can have four levels of structure: 1. primary structure, 2. secondary structure, 3. tertiary structure, and 4. quaternary structure.

114 Animation: Protein Structure Introduction

115 Animation: Primary Protein Structure

116 Animation: Secondary Protein Structure

117 Animation: Tertiary Protein Structure

118 Animation: Quaternary Protein Structure

119 Figure PRIMARY STRUCTURE +H 3 N Amino end Peptide bonds connect amino acids. Amino acids

120 Figure PRIMARY STRUCTURE +H 3 N Amino end Peptide bonds connect amino acids. Amino acids Two types of SECONDARY STRUCTURES Alpha helix Secondary structures are maintained by hydrogen bonds between atoms of the backbone. Beta pleated sheet

121 Figure PRIMARY STRUCTURE +H 3 N Amino end Peptide bonds connect amino acids. Amino acids Two types of SECONDARY STRUCTURES Alpha helix Secondary structures are maintained by hydrogen bonds between atoms of the backbone. TERTIARY STRUCTURE Beta pleated sheet Tertiary structure is stabilized by interactions between R groups.

122 Figure PRIMARY STRUCTURE +H 3 N Amino end Peptide bonds connect amino acids. Amino acids Two types of SECONDARY STRUCTURES Alpha helix Secondary structures are maintained by hydrogen bonds between atoms of the backbone. TERTIARY STRUCTURE Beta pleated sheet Tertiary structure is stabilized by interactions between R groups. QUATERNARY STRUCTURE Polypeptides are associated into a functional protein.

123 Figure PRIMARY STRUCTURE +H 3 N Amino end Peptide bonds connect amino acids. Amino acids Two types of SECONDARY STRUCTURES Alpha helix Secondary structures are maintained by hydrogen bonds between atoms of the backbone. TERTIARY STRUCTURE Beta pleated sheet Tertiary structure is stabilized by interactions between R groups. QUATERNARY STRUCTURE Polypeptides are associated into a functional protein.

124 Figure PRIMARY STRUCTURE +H 3 N Amino end Peptide bonds connect amino acids. Amino acids

125 Figure Two types of SECONDARY STRUCTURES Alpha helix Secondary structures are maintained by hydrogen bonds between atoms of the backbone. Beta pleated sheet

126 Figure TERTIARY STRUCTURE Tertiary structure is stabilized by interactions between R groups.

127 Figure QUATERNARY STRUCTURE Polypeptides are associated into a functional protein.

128 NUCLEIC ACIDS

129 3.15 DNA and RNA are the two types of nucleic acids The amino acid sequence of a polypeptide is programmed by a discrete unit of inheritance known as a gene. Genes consist of DNA (deoxyribonucleic acid), a type of nucleic acid. DNA is inherited from an organism s parents. DNA provides directions for its own replication. DNA programs a cell s activities by directing the synthesis of proteins.

130 3.15 DNA and RNA are the two types of nucleic acids DNA does not build proteins directly. DNA works through an intermediary, RNA (ribonucleic acid). DNA is transcribed into RNA in a cell s nucleus. RNA is translated into proteins in the cytoplasm.

131 Figure Gene DNA

132 Figure Gene DNA Transcription Nucleic acids RNA

133 Figure Gene DNA Transcription Nucleic acids RNA Amino acid Translation Protein

134 3.16 Nucleic acids are polymers of nucleotides DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotides. Nucleotides have three parts: 1. a five-carbon sugar called ribose in RNA and deoxyribose in DNA, 2. a phosphate group, and 3. a nitrogenous base.

135 Figure 3.16a Phosphate group Nitrogenous base (adenine) Sugar

136 3.16 Nucleic acids are polymers of nucleotides DNA nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G). RNA also has A, C, and G, but instead of T, it has uracil (U).

137 3.16 Nucleic acids are polymers of nucleotides A nucleic acid polymer, a polynucleotide, forms from the nucleotide monomers when the phosphate of one nucleotide bonds to the sugar of the next nucleotide by dehydration reactions. This produces a repeating sugar-phosphate backbone with protruding nitrogenous bases.

138 Figure 3.16b A Nucleotide T C G T Sugar-phosphate backbone

139 3.16 Nucleic acids are polymers of nucleotides RNA is usually a single polynucleotide strand. DNA is a double helix, in which two polynucleotide strands wrap around each other. The two strands are associated because particular bases always hydrogen-bond to one another. A pairs with T, and C pairs with G, producing base pairs.

140 Figure 3.16c C G C G T A C G Base pair A A T T A G T C T A A T

141 3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolution The majority of people stop producing the enzyme lactase in early childhood and do not easily digest the milk sugar lactose after childhood. Lactose tolerance represents a relatively recent mutation in the human genome and a survival advantage for human cultures with milk and dairy products available year-round.

142 3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolution Researchers identified three new mutations in 43 ethnic groups in East Africa that keep the lactase gene permanently turned on. The mutations are all different from each other and from the European mutation, appear to have occurred about 7,000 years ago, and occurred about the same time as the domestication of cattle in these regions.

143 Figure 3.17

144 You should now be able to 1. Describe the importance of carbon to life s molecular diversity. 2. Describe the chemical groups that are important to life. 3. Explain how a cell can make a variety of large molecules from a small set of molecules. 4. Define monosaccharides, disaccharides, and polysaccharides and explain their functions. 5. Define lipids, phospholipids, and steroids and explain their functions.

145 You should now be able to 6. Explain how trans fats are formed in food. Describe the evidence that suggests that eating trans fats is more unhealthy than consuming saturated fats. 7. Describe the chemical structure of proteins and the importance of proteins to cells. 8. Describe the chemical structure of nucleic acids and explain how they relate to inheritance. 9. Explain how lactose tolerance has evolved in humans.

146 Figure 3.UN01 H 2 O Dehydration Hydrolysis Short polymer Monomer Longer polymer H 2 O

147 Figure 3.UN02-0

148 Figure 3.UN02-1

149 Figure 3.UN02-2

150 Figure 3.UN03

151 Figure 3.UN04 Sucrose

152 Figure 3.UN05

153 Figure 3.UN06 Enzyme A Enzyme B Rate of reaction Temperature ( C)